Active polymer flooding for strongly heterogeneous reservoir associate with foam combination technology

After prolonged water flooding development, reservoir heterogeneity has become a serious issue. Polymer flooding, though the most mature and widely applied technique, faces adaptability challenges and struggles to achieve ideal oil displacement results. In response to strong heterogeneity in reservoirs, this paper adopts a "profile control before displacement" strategy, proposing an enhanced foam-active polymer profile control and displacement technology. Initially, a polymer-enhanced foam (AOS-DYG) is used to plug dominant flow channels, increasing the startup pressure in high-permeability layers and improving the sweep efficiency of subsequent fluids. Subsequently, an active polymer AM/AMPS/DMCA, capable of both enhancing sweep efficiency and displacement efficiency, is injected into secondary pore regions, ultimately forming an efficient chemical flooding system. Experimental results show that the optimal slug combination for the AOS-DYG + AM/AMPS/ DMCA chemical flooding system is 0.2 PV AOS-DYG+0.4 PV AM/AMPS/DMCA. In cores with a gas permeability of 1200 mD, this system enhanced oil recovery by 44.3%; in heterogeneous cores with a permeability contrast of 5-30, the EOR value ranged from 18.36% to 36.79%. This chemical system demonstrated an excellent oil displacement ability in strongly heterogeneous cores. The displacement mechanism in strongly heterogeneous reservoirs is investigated using a micro-etching visualization model and core nuclear magnetic resonance in-line displacement experiments. The AOS-DYG enhanced foam preferentially entered high-permeability layers, effectively plugging them and increasing the flow resistance in these areas, thereby expanding the sweep volume. This allows the subsequent active polymer AM/AMPS/DMCA to enter the lower permeability layers of the core, mobilizing the residual oil in low-permeability layers not reached during the water flooding stage, further confirming the feasibility of this chemical flooding system in EOR in strongly heterogeneous reservoirs.